My girlfriend cheated on me while I was on drugs?

My girlfriend and I have been with each other for going on three years now. For the past two years I was struggling with an addiction and I tried to get help but relapsed a few times. When I was high I did things that wasn't me, like I didn't treat her right and appreciate her or get her any gifts etc. Come to found out a few months ago she's been cheating on me with someone else and she left me for him, apparently he loves and appreciates her but I still don't think this was an excuse for him to cheat. Do you think that she's in the wrong here? Everyone is telling me that I did this to myself and that I had it coming but I don't think that's true